Piston-cylinder unit with device for determining position

Abstract

The present disclosure relates to a piston-cylinder unit with a device for determining position, the device comprising at least one exciter that is indirectly or directly electrically connected with the cylinder jacket and the cylinder piston of the piston-cylinder unit, and that excites the electrical oscillating circuit formed by the piston-cylinder unit and the contact lines to oscillate at its resonant frequency, it being possible to measure an electrical signal characterizing the resonant frequency on the piston-cylinder unit. The invention also relates to a construction machine or piece of hoisting equipment with such a piston-cylinder unit.

The invention claimed is: 
     
       1. A piston-cylinder unit with a device for determining position, the device comprising at least one exciter that is directly electrically connected with a cylinder jacket and a cylinder piston of the piston-cylinder unit, and that excites an electrical oscillating circuit formed by the piston-cylinder unit and contact lines to oscillate at its resonant frequency. 
     
     
       2. The piston-cylinder unit described in  claim 1 , wherein the exciter is an oscillator. 
     
     
       3. The piston-cylinder unit described in  claim 2 , wherein the oscillator is a Hartley oscillator. 
     
     
       4. The piston-cylinder unit described in  claim 1 , wherein the device for determining position is arranged at least partly inside the cylinder jacket. 
     
     
       5. The piston-cylinder unit described in  claim 1 , wherein the device further comprises an evaluation device which measures and evaluates an electrical signal characterizing the resonant frequency of the piston-cylinder unit. 
     
     
       6. The piston-cylinder unit described in  claim 1 , wherein the measured electrical signal comprises a voltage. 
     
     
       7. The piston-cylinder unit described in  claim 6 , further comprising an output device which outputs or displays the piston position. 
     
     
       8. The piston-cylinder unit described in  claim 1 , further comprising at least one shield to shield the device. 
     
     
       9. The piston-cylinder unit described in  claim 1 , wherein the device is structured to generate an electrical signal characterizing the resonant frequency of the piston-cylinder unit. 
     
     
       10. A construction machine or piece of hoisting equipment with a piston-cylinder unit including a device for determining position, the device including at least one exciter that is directly electrically connected with a cylinder jacket and a cylinder piston of the piston-cylinder unit, and that excites an electrical oscillating circuit formed by the piston-cylinder unit and contact lines to oscillate at its resonant frequency. 
     
     
       11. A piston-cylinder unit comprising:
 a cylinder jacket with a tubular shape that forms a hollow space therein; 
 a piston attached to a piston rod, housed within the hollow space of the cylinder jacket and separated from the cylinder jacket by a hydraulic medium; 
 an exciter electrically connected to the cylinder jacket and the piston rod, forming a series-resonant circuit in which the piston rod and cylinder jacket form a series inductance; and 
 an evaluation device connected to the series-resonant circuit, the evaluation device comprising a controller having a computer readable medium with instructions stored thereon which, when executed, cause the evaluation device to determine a resonant frequency of the series-resonant circuit and determine a position of the piston based on the resonant frequency. 
 
     
     
       12. The piston-cylinder unit described in  claim 11 , further comprising at least one additional inductance arranged between the exciter and the piston or between the exciter and the cylinder jacket. 
     
     
       13. The piston-cylinder unit described in  claim 11 , wherein the exciter is indirectly electrically connected with the cylinder jacket and the piston. 
     
     
       14. The piston-cylinder unit described in  claim 11 , wherein the exciter is directly electrically connected with the cylinder jacket and the piston. 
     
     
       15. The piston-cylinder unit described in  claim 8 , wherein the at least one shield is made of ferromagnetic material.